Description
Understanding plasma transport in the edge and Scrape-Off Layer (SOL) regions is crucial for optimizing plasma performance and predicting heat loads on plasma-facing components. Limiter configuration, encountered in the start-up phase in all tokamaks, requires a precise characterization of power and particle decay lengths, especially for extrapolating to future devices like ITER. Simultaneously, it offers a simplified geometry for comparing experimental results with transport theory and fundamental physics.
This study investigates transport across various WEST plasma regimes in limiter configuration. Furthermore, we benchmark the SOLEDGE3X transport code against its HDG finite element implementation to evaluate the consistency and accuracy of its numerical results.
The analysis is carried out on WEST discharges specifically designed to study the limiter configuration, with a toroidal magnetic field of about 3.7 T, plasma currents $I_{p}$ of 300 kA and 700 kA respectively and corresponding SOL power levels of approximately 200 kW and 600 kW. The study relies on Langmuir probe measurements, which in WEST are flush-mounted with the internal tiles, as foreseen and required for ITER diagnostics.
We performed edge modeling to estimate transport profiles matching experimental measurements across various plasma conditions. We study transport behavior in the near and far SOL to evaluate decay lengths in both regions, which are then compared with values evaluated from present scaling laws. Finally, we performed a series of simulations varying plasma power, density and transport coefficients to isolate their individual effects on the decay length accounting for non-linear ionization and recombination effects.